Silica Aerogels are a seemingly new creation, when in fact, they have been in existence (theoretically) for nearly 70 years. In 1931, Steven. S. Kistler first set out to prove that a “gel” contained a continuous solid network of the same size and shape as the wet gel. The obvious way to prove this hypothesis was to remove the liquid from the wet gel without damaging the solid component. “Obviously, if one wishes to produce an aerogel [Kistler is credited with coining the term “aerogel”], he must replace the liquid with air by some means in which the surface of the liquid is never permitted to recede within the gel. If a liquid is held under pressure always greater than the vapor pressure, and the temperature is raised, it will be transformed at the critical temperature into a gas without two phases having been present at any time.” (S. S. Kistler, J. Phys. Chem. 34, 52, 1932).
Further advancement in this research was prolonged until the late 70's, when the specific, correct procedure for creating Aerogels was developed. Basically, and Aerogel is simply a Silica water-based gel, that has been exchanged with ethanol (to remove water), then supercritically dried (to remove the ethanol) in order to excavate ALL liquid, leaving a 3 dimensional matrix, resulting in a retention of surface area and in increase in free-space. Amazing Characteristics of Aerogel include its low solid percentage (0.13-15% solid, typically 95% air), high internal surface area (600-100 m2/g), a low index of refraction (1.0-1.05, close to that of AIR) and high thermal tolerance (shrinkage begins at 500° C.; melting point 1200° C.). Unfortunately, it is somewhat unstable, with a maximum tensile strength of 48 kPa (48,000 Pa), which accounts for its brittleness.
Carbon Nanotubes (CNT), on the other hand, are a relatively new discovery. These stem from the detection of a class of allotropes of carbon, the fullerenes (which are perfect “cages” of Carbon atoms in geometric configurations, usually even-numbered between 60-80). Carbon fullerenes can be located in soot as produced by the Kratschmer-Huffman (a machine which, along with high-temperatures, arcs electricity between two sticks of carbon) arc process. Single-wall nanotubes can also be found in the arc, usually in the presence of a metal catalyst. The nanotubes are found in the matted soot deposited on the reaction chamber wall. Japanese scientist Sumio Iijima is credited with discovering the nano-size tubes during experimentation in late 1991. Recently, nanotubes with unique characteristics and unusually small/large areas/diameters can be produced using a laser burning technique, which produces carbon “ropes”. Carbon Nanotubes (CNTs) consist of concentric shells of graphite. Each shell can be thought of as one layer of a conventional graphite structure rolled up into a cylinder such that the lattice of carbon atoms remains continuous around the circumference. These are known as Multi-Walled Nanotubes (MWNT), whereas Single-Walled Nanotubes (SWNT) have only a single “shell of graphite”. CNTs are usually 1-50 nanometers in diameter and typically a few microns long, although recently SWNTs have been grown to over 300 microns. Even though the nanotubes are extremely small, they are currently renown as the stiffest, strongest materials known, possessing the ability to be bent and warped without breaking and then be bent back into their original shape. To express this numerically, the nanotubes have an average tensile strength of 1.3 TPa (1,300,000,000,000 Pa), able to sustain a critical stress of 156 GPa (156,000,000,000 Pa) before collapsing plastically.
Examples of similar inventions with similar application as the embodiments described herein include Hydrocarbon (Hydrogen)/Air Aerogel Catalyzed Carbon Electrode Fuel System Cell System: U.S. Pat. No. 5,429,886, issued Jul. 4, 1995; Carbon Aerogel Electrodes For Direct Energy Conversion, U.S. Pat. No. 5,601,938, issued Feb. 11, 1997; Organic Aerogel Microspheres, U.S. Pat. No. 5,908,896, issued Jun. 1, 1999; and Metal Alloy Laded Carbon Aerogel Hydrogen Hydride Battery, U.S. Pat. No. 5,366,828, issued Nov. 22, 1994.